Although it is thought that humans don’t need cholesterol in their diet—the body makes all it needs—it is an important component in the cell membranes of animals. Cholesterol, a lipid-based molecule (steroid), actually has two functions: 1) to help stabilize the membrane, and 2) to maintain membrane flexibility as temperature changes. Normally the human body is capable of producing all the cholesterol it needs. Dietary ingestion of excess saturated fats and cholesterol is currently thought to be the source of the plaque that builds up in arteries and can cause heart attacks and strokes. Dietary cholesterol can be found in all animal sources, including shellfish. Plant phytosterols have the same function as cholesterol found in animals, but they do not affect the human body in the same way.